The boys nodded.
“This,” he went on, “moves the cross hairs. And these—” he gestured to a pair of screws—“turn the whole mount any degree you want.” He grinned at them. “Simple, eh?”
“One more question.”
“Shoot.”
“How do you know how much to turn it? All that business about a minute of angle having a value of about half an inch at fifty yards—that’s all Greek to me.”
“You remember your geometry, don’t you, Mike? An angle cuts off an arc. And you know how to measure an arc.”
Mike looked surprised. “In minutes and degrees,” he said, with sudden comprehension.
“There’s your answer. Now I’ll grant you,” Mr. Cook added, “that I just happen to know how big an arc an angle makes at various distances. But that’s only because I’ve been working with guns for a long time. And if I didn’t know, I could always figure it out. The rest,” he said, standing up, “is trial and error. Let’s see how we did.”
With a single easy motion, he hunched over the rifle and, in rapid succession, poured three shots into the bull’s-eye. “Well?” he demanded as he straightened up.
Sandy peered through the binoculars. Three holes bunched together in the space of a dime had perforated the plastic directly above the target.